The basic idea is this: yes, it isn't good that we route our carbon vapors back into the intake....but the little k&N's do not provide vacuum suction to remove it from the head, and they do not vent enough. There are ways to efficiently vent but those small breathers don't get the job done...and when compared to the stock closed system, the stock is better because it provides vaccum; just clean your throttle body once in awhile...not too much trouble.